We lost nearly 75 per cent of the insect population just in the last 20 years: Reasons unknown : Did you know?

In recent years, it became clear that the insect populations such as those of butterflies and bees were declining in Western Europe and North America. “However, the fact that flying insects are decreasing at such a high rate in such a large area is an even more alarming discovery,” stated project leader at the Radboud University, Hans de Kroon.

Entomologists (insect researchers) in Krefeld, Germany, led by Martin Sorg and Heinz Schwan, collected data over the past 27 years in 63 different places within nature reserves across Germany. Flying insects were trapped in malaise traps and the total biomass was then weighed and compared. The researchers from Nijmegen, Germany and England have now been able to analyse this treasure trove of data for the first time.

More about the research:

The researchers discovered an average decline of 76 per cent in the total insect mass

In the middle of summer, when insect numbers peak, the decline was even more severe at 82 per cent

According to Caspar Hallmann from Radboud University who performed the statistical analyses, “All these areas are protected and most of them are managed nature reserves. Yet, this dramatic decline has occurred.”

The exact causes of the decline are still unclear. Changes in the weather, landscape and plant variety in these areas are unable to explain this

The weather might explain many of the fluctuations within the season and between the years, but it doesn’t explain the rapid downward trend

Since 1989, in 63 nature reserves in Germany, the total biomass of flying insects has decreased by more than 75 per cent. This decrease has long been suspected but has turned out to be more severe than previously thought

Time to wake-up

As entire ecosystems are dependent on insects for food and as pollinators, it places the decline of insect eating birds and mammals in a new context. We can barely imagine what would happen if this downward trend continues unabated.

Because the causes of the decline are not yet known, it is difficult to take any concrete measures. The researchers hope that these findings will be seen as a wake-up call and prompt more research into the causes and support for long-term monitoring.

Ecologists from Radboud University together with German and English colleagues published these findings in the scientific journal PLoS ONE.

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